The XMM-LSS survey: The Class 1 cluster sample over the initial 5 deg 2 and its cosmological modelling

F. Pacaud*, M. Pierre, C. Adami, B. Altieri, S. Andreon, L. Chiappetti, A. Detal, P. A. Duc, G. Galaz, A. Gueguen, J. P. Le Fèvre, G. Hertling, C. Libbrecht, J. B. Melin, T. J. Ponman, H. Quintana, A. Refregier, P. G. Sprimont, J. Surdej, I. ValtchanovJ. P. Willis, D. Alloin, M. Birkinshaw, M. N. Bremer, O. Garcet, C. Jean, L. R. Jones, O. Le Fèvre, D. MacCagni, A. Mazure, D. Proust, H. J.A. Röttgering, G. Trinchieri

*Corresponding author for this work

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120 Citations (Scopus)


We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5 deg2 out to a redshift of z = 1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well-defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses, obtained from dedicated spatial and spectral fitting. The cluster distribution peaks around z = 0.3 and T = 1.5 keV, half of the objects being groups with a temperature below 2 keV. Our LX-T(z) relation points towards self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z = 1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well-monitored selection function allowed us to demonstrate that the inclusion of selection effects is essential for the correct determination of the evolution of the LX-T relation, which may explain the contradictory results from previous studies. Extensive simulations show that extending the survey area to 10 deg2 has the potential to exclude the non-evolution hypothesis, but those constraints on more refined intracluster medium models will probably be limited by the large intrinsic dispersion of the LX-T relation, whatever be the sample size. We further demonstrate that increasing the dispersion in the scaling laws increases the number of detectable clusters, hence generating further degeneracy [in addition to σ8, Ωm, LX-T(z)] in the cosmological interpretation of the cluster number counts. We provide useful empirical formulae for the cluster mass-flux and mass-count rate relations as well as a comparison between the XMM-LSS mass sensitivity and that of forthcoming Sunyaev-Zel'dovich surveys.

Original languageEnglish
Pages (from-to)1289-1308
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 1 Dec 2007


  • Cosmological parameters
  • Large-scale structure of Universe
  • Surveys
  • X-rays: galaxies: clusters

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    Pacaud, F., Pierre, M., Adami, C., Altieri, B., Andreon, S., Chiappetti, L., Detal, A., Duc, P. A., Galaz, G., Gueguen, A., Le Fèvre, J. P., Hertling, G., Libbrecht, C., Melin, J. B., Ponman, T. J., Quintana, H., Refregier, A., Sprimont, P. G., Surdej, J., ... Trinchieri, G. (2007). The XMM-LSS survey: The Class 1 cluster sample over the initial 5 deg 2 and its cosmological modelling. Monthly Notices of the Royal Astronomical Society, 382(3), 1289-1308.